Many techniques are known for the production of hydrofluorocarbons (HFCs) and fluorocarbons (FCs). Certain prior methods involve fluorinating chlorinated organic compounds to produce the desired HFC or FC compounds, and then recovering the desired compounds through distillation. Although both liquid phase and vapor phase processes are available, vapor phase catalytic reactions are preferred in certain applications. For example, in certain difluoromethane (HFC-32) production processes, a chlorinated organic compound, such as, for example, dichloromethane (HCC-30), and a fluorinating agent, such as, for example, hydrogen fluoride (HF), are reacted, usually after preheating, in the presence of a fluorination catalyst to generate a reaction product stream.
The desired HFC or FC compound is recovered by the use of distillation from the reaction product stream, which also contains other materials such as unreacted HF and byproducts of the reaction. Distillation is well known in the art and typically involves the use of distillation means, such as a packed column or one with trays, operated at pressures and temperatures selected to separate the reaction product stream into a stream relatively rich in the desired compound and stream relatively rich in compounds that are not desired in the finished product, such as unreacted components and unwanted byproducts. Distillation pressure and temperature are interrelated such that higher operating pressures generally correspond to higher distillation temperatures. Distillation temperatures dictate the heating and cooling requirements of the fractionation tower.
The desirability of a fluorination process is generally linked to the yield and product purity resulting from the process. For example, if the desired product is the HFC difluoromethane, the amount of such product which is recovered from the reaction product should ordinarily be as high as possible, and the type and amount of impurities contained in the final product stream should be as low as possible. While prior processes have achieved a certain level of success as measured by yield and product purity, applicants have come to appreciate that certain features of the prior art may raise barriers against continuing improvement of product yield and purity.
For example, many prior art methods of producing HFCs and FCs suffer from the problem of catalyst deactivation during fluorination, which leads to lower yields. In an attempt to maintain catalyst activity, a regenerating agent, such as chlorine, is typically co-fed with the reactants into the reactor in a continuous, semi-continuous or batch fashion. Applicants have come to recognize, however, that the addition of chlorine can, in certain circumstances, add to the formation of generally undesirable byproducts, which in turn can have a negative effect on yield and product quality.